Nearly all facilities that use electricity are equipped with a system containing fuses and/or circuit breakers, thus applied to cut off electrical supply when an electrical fault occurs. These devices operate by sensing excess current or other current-related phenomena, which typically occurs due to a short circuit, connection/disconnection of loads, short-term wiring disconnections or other electrical faults. (For example, arc-fault circuit interrupters detect current changes that are typical of arc-faults, while ground-fault circuit interrupters compare incoming current to outgoing current.) Despite the fact that modern buildings and other facilities are equipped with modern electrical-fire prevention devices, improper power supply to loads in a facility are common and remain a severe hazard. According to the U.S. Fire Administration, for example, home electrical problems have recently accounted for 90,000 fires each year, causing over 700 deaths and $700 million in property losses. Such fires result from faulty wiring, from faults in appliances connected to the wiring, faults in the connections between the wiring itself or from any other part of the electrical system that conducts electrical current to the electrical loads. The electrical disturbance can be intermittent or fixed, thus leading to a time-to-time disturbance in the required operation of the electrical loads or preventing them from working at all.
Many electrical fires are a direct result of an electrical fault, in which the temperature of an electrical conductor significantly increases. The power dissipated by a piece of an electrical conductor is proportional to the voltage across the piece of conductor and the current through the conductor.
It is known in the art to measure the voltage and current consumed by a particular electrical appliance; such measurements indicate the total power consumed by a user and enable to bill him accordingly. Numerous attempts for an early detection of electrical faults have been made in recent years. Examples of existing electrical-fire prevention devices are the fuse, the circuit breaker and the Arc-Fault Circuit Interrupter. The fuse is a piece of wire designed to melt when the current through it exceeds a pre-defined level and as a result de-energize the circuit connected to it. The circuit breaker also checks whether the current passing through it for not exceeding a pre-defined level. The Arc-Fault Circuit Interrupter checks the current passing through it in order to find current and/or voltage changes which are indicative of an arc-fault, in addition to checking whether the current passing through it for not exceeding a pre-defined level. However, these devices are designed to treat all the resistance or impedance of the circuit as one equivalent resistor, and therefore have no indication of the amount of energy dissipation over each of the conductors, resistors, capacitors, coils, and other parts comprising the circuit. In addition, aging of the wiring within a facility creates “parasitic” resistors, which consume additional power. Existing protection devices lack the ability to measure power ratio between a desired load and a parasitic one. In some cases, the parasitic resistance acts as a current-limiter and prevents the current in the faulty circuit from being out of range of a pre-defined tripping level of the fuses or circuit-breakers that are in use in that circuit. These cases are typical to electrical circuits in which the intended load has a small resistance (e.g. a mechanically-stuck motor that exhibits very low DC resistance). Such cases can also be found in faulty wiring problems that create a short-circuit, whereas the series-connection with the parasitic resistance limits the current through the shortened circuit to be below the tripping level of the fuse or the circuit-breakers being used.
In other cases, the temperature increase over the parasitic resistance is itself a cause for a fire. These cases are typical to electrical circuits in which the intended load is a “pure resistance” load—like a baking oven. The increasing ratio of the parasitic resistance as part of the overall circuit resistance causes an increased percentage of the total circuit power to be dissipated by the parasitic resistance. This leads to a significant increase in the temperature of the parasitic loads of the electrical system and may ignite a fire.
In some devices, the checking process is performed by a bi-metal conductor that bends and cuts the electrical current when the current through it exceeds a predefined limit. In other devices—the checking process is performed by an electromagnet that develops a magnetic power, whereas the magnetic power is proportional to the current passing through it. The existence of magnetic power affects the mechanical connection within the device and as a result the electrical current to the load is stopped. The protective device is implemented within the electrical circuit in such a manner that it is serially connected to appropriate load. As a result, current passing through the protection device causes dissipation of energy across the protection device itself. This may lead to heating of that protection device and additional undesired phenomena such as corrosion, carbonization of conductors and mechanical deformation of the different parts comprising the protective device itself. Hence, the protection device's capability to detect an electrical-current fault is severely affected.
Furthermore, different checks are applied for detecting an electrical fault in a facility, whereas these checks can be due to regulations, a suspect of an electrical fault, due to indications of a fault whose location is not determined, for preventive-maintenance activities or similar circumstances. Among these tests are the infra-red photography of wiring, switch-panels and other appliances. Another test is the ultrasonic detection of wiring/appliances problems. However, these checks require special equipment, which does not operate constantly as part of the inspected facility. Therefore, these appliances can only detect a problem that occurs when such a specific test equipment is set to perform the tests.
Additional attempts include devices, which are provided for detecting an electrical fault by measuring current. Such devices include the AFCI (Arc-Fault Circuit Interrupter), which checks for indications of electrical-arcing in the wire, the ELCI (Equipment Leakage Circuit Interrupter), the GFCI (Ground-Fault Circuit Interrupter), which monitors the electricity flowing in a circuit and if the amount flowing into the circuit differs from the amount returning this interrupter shut off the current, the LCDI (Leakage Current Detection and Interruption), which is built as part of a power-plug, the ALCI (Appliance Leakage Circuit Interrupter), which is implemented as an integrated part within the appliance, and the IDCI (Immersion Detection Circuit Interrupter), which detects immersion of an electrical appliance (like a hair-dryer) in water.
Prior art devices include U.S. Pat. No. 6,445,188, whose disclosure is incorporated herein by reference, describes an intelligent, self-monitoring AC power plug, which contains current and voltage sensors. The plug includes a miniature printed circuit board, with a filtered power supply, microcontroller, and external interface. Based on the combined readings from the voltage sensor and the current sensor, an embedded program running on the microcontroller can determine the power being consumed by the loading device. The plug may be connected to a special interface connector in order for data to be exchanged with a computer. The interface also allows for networking of several plug devices to a central reader.
As another example, U.S. Pat. No. 5,315,236 describes a power meter that plugs into an electric socket and has a socket for receiving the plug of an electric appliance. Alternatively, the power meter may be part of an electric wall switch or wall socket. U.S. Pat. No. 5,869,960 describes a similar sort of device. Other references relating to voltage testing and power monitoring include U.S. Pat. Nos. 4,672,555, 4,858,141, 4,884,022 and 5,196,982. The disclosures of all of these patents are incorporated herein by reference.
One of the fundamental drawbacks common to all above-mentioned prior art devices is the fact that they all operate post factum. In other words, they only detect the faulty condition after it has already happened. In many cases this is usually too late to prevent the risk of fire from materializing.
The present invention takes a pre-factual approach to preventing the said risks. The invention detects the preconditions indicating a situation that might lead to unreasonable voltage-drop in the circuit, glowing and finally sparkling. Monitoring is done while the electrical distribution system is in regular use, with problematic voltage drops being the only fault-indication existing In addition, the present invention is capable of detecting for how long a circuit-breaker, AFCI or an equivalent device—did not trip. Long periods of time of usage without any tripping of these devices might be indicative of carbonization and micro-welding of contacts in the protection devices themselves.
A further drawback of prior art device is that they are all current-oriented devices. The problem with protection systems based on measuring current is that parasitic resistance in the electrical circuit acts as a current limiter which prevents the protection devices from tripping—even when the original load becomes a short circuit. This is because the protection devices measure a current common to the parasitic and the original loads as they are serially connected.
The current-oriented protection circuits hypothesis is of a faulty circuit to exhibit a “short-circuit” protection, with no parasitic load in it. The terminology used—of detecting short-circuits only—emphasizes the limited capabilities of such systems.
The fact that the existing protection systems are rated in terms of current, not voltage-drop percentage or absolute voltages—indicates that these protection devices measure current only.
Yet another aspect differentiating current measurements from voltage measurements: by measuring currents—faulty conditions may be detected only when currents EXCEED a predefined limit, whereas measuring voltages may detect faulty conditions that cause the measured voltage to be too low rather than too high.
It should be noted in particular that none of the existing methodologies propose a system for an early detection of electrical fault in an electrical system by monitoring voltage levels in parallel to loads within a facility.
It is thus the object of this invention to propose a system, apparatus and method that provides an early and automatic detection of electrical faults in a facility by monitoring local voltage levels (in parallel to the loads) and continuity measurements of electrical-power presence at one or more points along the electrical circuit of the electrical system of said facility.
It is yet another object of the present invention to further determine the type and specific location of the electrical fault which is most likely within the facility.